<?php
$con=mysqli_connect("mysql13.000webhost.com","a7898507_usuario","abc123","a7898507_azucar");
$mail = $_POST['correo'];
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
if (!$mail) { echo 'Complete el campo mail'; }
else {
	$sql="INSERT INTO clientes (correo)
	VALUES
	('$_POST[correo]')";  
	if (!mysqli_query($con,$sql))
	  {
	  die('Error: ' . mysqli_error($con));
	  }
	echo "1 record added";
}  

mysqli_close($con);
?>